Improved riser tensioner bearing system

ABSTRACT

A serial bearing ( 300 ) for a riser tensioner system is provided. The serial bearing improves lateral and axial load performance when severe side-loads are transferred to the riser tensioner system.

PRIORITY CLAIM

The present application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/898,860, filed Nov. 1, 2013, the disclosure of which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The subject matter disclosed herein relates to offshore oil platforms and support structures. More particularly, the subject matter disclosed herein relates to devices, systems, and methods for reducing riser tensioner system failures attributable to side-loads applied to hydraulic or pneumatic cylinders of riser tensioner systems.

BACKGROUND

Riser tensioner systems are subjected to side-loading during normal operations. These side-loads, also known as lateral loads or bending loads, are forces impacting the riser tensioner system. In many designs, the riser tensioner systems include hydraulic or pneumatic cylinders. Most vertically positioned riser tensioner systems are vulnerable to being damaged by these side-loads as the result of oceanic wave energy being transferred to the riser tensioner systems due to the ebb and flow of the waves around these riser tensioner systems and the components supported by the riser tensioner systems. When the oceanic waves have more energy the forces transferred to the riser tensioner systems increase. There is a point where the oceanic waves create failure modes of the riser tensioner systems due to the high energy forces acting upon the riser tensioner systems as severe side-loads. This is a case of excessive side-loads impacting the hydraulic or pneumatic cylinders.

One failure mode for hydraulic or pneumatic cylinders, hereinafter referred to as cylinders, occurs when the cylinder is subjected to high lateral or bending loads which exceed the load bearing capabilities of the cylinder's sealing mechanism. These excessive loads can compromise the sealing mechanism, thereby reducing the life of the cylinder. Another failure mode for cylinders occurs when high lateral or bending loads exceed the load bearing capabilities of a piston rod of the cylinder, thereby potentially preventing desired actuation of the piston rod of the cylinder. In such cases maintenance or replacement efforts are required, which significantly impact associated lost time and financial expenses.

Because the available riser tensioner systems do not have a sufficient ability to resist the high-side loads the lifetime of the riser tensioner systems are reduced. A crude approach to solving this problem is to design a more robust cylinder and seal capable of withstanding the high side-loads. Unfortunately, this approach increases the physical size and the cost of the riser tensioner system. Thus, this approach is less economically feasible to manufacture and creates immense handling and installation issues.

What is needed is a riser tensioner system which provides the ability to withstand high side-loading conditions, provide beneficial performance while maintaining economical manufacturability and provide robust life of service.

SUMMARY

In one aspect a riser tensioner system utilizing a serial elastomeric bearing arrangement is provided. The serial elastomeric bearing includes a spherical bearing which provides for cocking compliance in series with a radial bearing of a riser tensioner system thereby providing for lateral compliance in high side-load conditions. The combined bearing, a series bearing, has a high axial stiffness providing for the efficient transmission of axial loads. The cocking compliance is provided by a spherical bearing which in turn provides protection from high side-loads. The lateral compliance from a spherical bearing provides for additional motion accommodation. The additional motion accommodation protects the cylinder from particularly severe side-loads. As such, the possibility for cylinder failure is reduced, as is the need to design a higher cost, more robust cylinder.

In one aspect, the series bearing is directly bonded using typical elastomer manufacturing methods. In another aspect, a sequential bonding process using structural adhesives is used to fabricate the series bearing in a modular manner. Sequential bonding provides for rapid application design iterations and facilitates using the rubber bearing in multiple arrangements. Sequential bonding can reduce design manufacturing tooling efforts and costs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side view an offshore a hydrocarbon system including a plurality of riser tensioner systems that each include a series bearing.

FIG. 2A is an orthogonal side view of a series bearing of the riser tensioner system of FIG. 1.

FIG. 2B is an oblique lower-side view of the series bearing of FIG. 2A.

FIG. 2C is an orthogonal cross-sectional view of the series bearing of FIG. 2A taken along cutting line 2C-2C of FIG. 2B.

FIG. 3 is an orthogonal cutaway view of an alternative radial bearing stack.

DETAILED DESCRIPTION

Referring now to FIG. 1, a hydrocarbon system 100 for use in discovering and producing hydrocarbons or petroleum materials is illustrated. The hydrocarbon system 100 is located offshore and is tethered to the ocean floor 102. The hydrocarbon system 100 includes buoyant platform foundations 104 that are tethered to the ocean floor 102 by tendons 106. The platform foundations 104 support a deck foundation 108. The hydrocarbon system 100 further includes a well template 110 from which multiple risers 112 rise up to the deck foundation 108. Each riser 112 is associated with separate wells or wellbores formed in the earth below the well template 110. The hydrocarbon system 100 also includes a plurality of riser tensioner systems 200, one riser tensioner system 200 for each of the risers 112. The riser tensioner systems 200 are configured to accommodate relative movement between the risers 112 and the platform foundations 104 or deck foundation 108 to prevent buckling of the risers 112.

The riser tensioner systems 200 of hydrocarbon system 100 include a vertical support frame having legs configured for connection to the deck foundation 108. The riser tensioner systems 200 include a plurality of vertically oriented cylinders which each comprise a piston rod that extends and retracts vertically relative to the support frame. Each riser tensioner system 200 includes a collar configured to engage with a riser 112. The collar has a plurality of laterally extending arms. Each arm extends laterally to a location vertically above an associated one of the cylinders. The piston rods are attached to their associated arms with a serial bearing 300. The serial bearings 300 accommodate both relative lateral movement between the piston rods and the collar as well as relative cocking movement between the piston rods and the collar. Accordingly, the serial bearings 300 collectively accommodate relative movement between the riser 112 and the cylinders of the riser tensioner systems 200.

Referring now to FIGS. 2A-2C, an orthogonal side view, an oblique lower view, and an orthogonal cross-sectional view of a serial bearing 300 of the riser tensioner systems 200 are shown, respectively. The serial bearing 300 includes a radial bearing stack 302 and a spherical bearing stack 304 located in series to provide lateral and cocking compliance or movement, respectively. The radial bearing stack 302 is a high capacity laminate (HCL) bearing manufactured with known HCL technologies. The radial bearing stack 302 has elastomeric elements 306 and shim elements 308. The elastomeric elements 306 and the shim elements 308 are disc shaped. The spherical bearing stack 304 is an HCL bearing manufactured with known HCL technologies. The spherical bearing stack 304 has elastomeric elements 310 and shim elements 312. The elastomeric elements 310 and the shim elements 312 are shaped as spherical sections. Series bearing 300 is customizable for the particular end user's requirements. Spherical bearing stack 304 accommodates cocking motions and radial bearing stack 302 accommodates radial motions relative to riser 112. In alternative embodiments, a spherical bearing stack is designed to allow radial motion in addition to the radial motion allowed by the radial bearing stack 302. The performance characteristics of spring rates and motions allowed by the serial bearing 300 can be controlled by adding or removing elastomeric elements 306, 310 and shim elements 308, 312. In this case the spring rates are selected for a given set of environmental conditions defined by the user. The spring rates are modifiable to provide softer or stiffer spring rates, depending upon the end user's needs.

The radial bearing stack 302 is mounted between a radial bearing mount 314 and an intermediate mount 316. The radial bearing mount 314 includes a flat and rigid disc having a diameter at least as large as a diameter of the radial bearing stack 304. The intermediate mount 316 includes a rigid component having a flat radial bearing interface surface 318 connected to the radial bearing stack 302 and a spherical section shaped concave surface 320 connected to the spherical bearing stack 304. The spherical bearing stack 304 is mounted between the intermediate mount 316 and a spherical bearing mount 322. The spherical bearing mount 322 includes a spherical section shaped convex surface 324 connected to the spherical bearing stack 304. The spherical bearing mount 322 also includes a riser interface 326 connected to a piston rod or other portion of a cylinder. The radial bearing mount 314 also includes an arm interface 328 connected to an arm of a collar. The serial bearing 300 provides lateral and cocking compliance while maintaining high axial stiffness for transmission of axial loads. Serial bearing 300 reduces severe side-loads caused by extreme weather events (green impact waves), etc., that would otherwise result in high lateral loading of cylinder seals which adversely affects the seal life. Cocking compliance provides elastomeric bearing protection from severe side-loads while the radial bearing stack 304 provides significantly increased compliance to protect the riser tensioner systems 200 from particularly severe side-loads. The radial bearing mount 314 is welded or otherwise rigidly fixed to an arm of a collar. In alternative embodiments, the radial bearing mount is sized to overhang or extend beyond the radial bearing stack (not shown) so that through holes are provided to receive bolts or other fasteners that are configured to aid in attaching the radial bearing mount to the arm of a collar. Similarly, the spherical bearing mount 322 comprises recesses 328 or apertures configured to aid in attaching the spherical bearing 322 to a riser 112 or to another component rigidly attached to a riser 112. In alternative embodiments, the vertical orientation of the serial bearing 300 may be reversed to similarly provide the above-described lateral and cocking compliance.

In a preferred embodiment, spherical bearing stack 304 with elastomeric elements 310 and shim elements 312 is designed to have a specific stiffness. Preferably, spherical bearing stack 304 has a radial spring rate of about 781,000 lbf/in (about 136,774.1 KN/m), a torsional spring rate of about 1900 in-lbf/deg (about 215 Nm/deg), a cocking spring rate of about 4000 in-lbf/deg (about 452 Nm/deg), and an axial spring rate of about 4.7×10⁶ lbf/in (about 823,096.1 KN/m). The axial and radial spring rates of the spherical bearing stack 304 are nonlinear, where an increase in load yields an increase in the stiffness. Typically, the stiffness for the cocking spring rate will be less than 4000 in-lbf/deg (about 452 Nm/deg). The maximum cocking motion of spherical bearing stack 304 is about +/−15 degrees from the vertical. These stiffness values are added in series with the radial bearing values.

In a preferred embodiment, radial bearing stack 302 has stiffness values for compression, cocking and radial (shear) forces. For compression, radial bearing stack 302 has a value of about 1.2×10⁷ lbf/in (about 2,101,522 KN/m). For cocking, radial bearing stack 302 has a value of about 9×10⁵ lbf ft/deg (about 1,220.2 KNm/deg). For radial (shear) radial bearing stack 302 has a value of about 22,000 lbf/in (about 3,852.8 KN/m). The axial (compression) and cocking spring rates of radial bearing stack 302 are nonlinear, where an increase in load yields an increase in the stiffness. In a preferred embodiment, radial bearing stack 302 has radial motion capabilities of about 1.125 inches to about 1.875 inches (about 2.86 centimeters to about 4.76 centimeters) under survival conditions and about 0.160 inches (about 0.41 centimeters) under fatigue conditions.

Spherical bearing stack 304 and radial bearing stack 302 are capable of being manufactured with direct bonding or sequential bonding. The sequential bonding process uses structural adhesives to fabricate the serial bearing 300 in a modular manner. Sequential bonding provides for rapid application design iterations and facilitates using the elastomeric element 306 in multiple arrangements. Sequential bonding may reduce design manufacturing tooling efforts and costs.

Referring now to FIG. 3, an orthogonal cutaway view of an alternative radial bearing stack 400 is shown. The radial bearing stack has an outside diameter of 16 inches (about 40.6 centimeters), a 4.813 inch (about 12.23 centimeters) inner diameter and an 8 inch (about 20.3 centimeters) thickness to yield a radial stiffness of 2200 lb/in (about 385,279 N/m). The radial bearing stack 400 includes elastomeric element rings 402 and shim rings 404.

Other embodiments of the current invention will be apparent to those skilled in the art from a consideration of this specification or practice of the invention disclosed herein. Thus, the foregoing specification is considered merely exemplary of the current invention with the true scope thereof being defined by the following claims. 

What is claimed is:
 1. A serial bearing for a riser tensioner system, said serial bearing including: a radial bearing mount; a spherical bearing mount; an intermediate mount disposed between the radial bearing mount and the spherical bearing mount; a radial bearing stack disposed between the radial bearing mount and the intermediate mount; and a spherical bearing stack disposed between the spherical bearing mount and the intermediate mount.
 2. The serial bearing of claim 1, wherein the radial bearing stack includes a high capacity laminate (HCL).
 3. The serial bearing of claim 2, wherein said HCL is formed using direct bonding.
 4. The serial bearing of claim 2, wherein said HCL is formed using sequential bonding.
 5. The serial bearing of claim 1, wherein the spherical bearing stack includes a high capacity laminate (HCL).
 6. The serial bearing of claim 5, wherein said HCL is formed using direct bonding.
 7. The serial bearing of claim 5, wherein said HCL is formed using sequential bonding.
 8. The serial bearing of claim 1, wherein said spherical bearing stack has a spring rate of about 1.2×10⁷ lbf/inch in compression, about 22,000 lbf/inch in shear, and about 9×10⁵ lb·ft/deg for cocking.
 9. The serial bearing of claim 1, wherein said spherical bearing stack has a radial spring rate of about 781,000 lbf/inch, a torsional spring rate of about 1900 in-lbf/deg, a cocking spring rate of about 4000 in-lbf/deg, and an axial spring rate of about 4.7×10⁶ lbf/inch.
 10. The serial bearing of claim 9, where said axial spring rate and said radial spring stack are nonlinear and are configured to increase in a stiffness as a load acting upon said spherical bearing stack increases.
 11. The serial bearing of claim 9, wherein said spherical bearing stack has cocking spring rate less than or equal to about 4000 in-lbf/deg.
 12. The serial bearing of claim 1, wherein at least one of the radial bearing mount and the spherical bearing mount are configured for connection to a riser.
 13. The serial bearing of claim 12, wherein a cocking motion of said spherical bearing stack is about +/−15 degrees from a vertical direction relative to said riser.
 14. The serial bearing of claim 1, wherein the radial bearing stack includes at least one of ring shaped elastomeric elements and ring shaped shim elements. 